1. Field of the Invention
The present invention relates to an optical signal transfer device which transfers signals between a receiver system and a transmitter system which are relatively rotated around a single axial line.
2. Description of the Related Art
In surveying work in association with civil engineering work, use of surveying equipment with a ranging unit rotatable on a base (support unit) is well known. In order to control a light adjuster in the ranging unit, the surveying equipment is required to be able to transfer a control signal from an arithmetic controller of the base unit to the light adjuster of the ranging unit in rotation, that is, to transfer signals between the base unit and the ranging unit as a rotary element. For this purpose, there is a slip ring having a contact slidably contacting with the rotary element to electrically connect an output terminal of the base unit and an input terminal of the ranging unit.
Generally, the surveying equipment is required to accurately transfer control signals from the arithmetic controller to the light adjuster while the ranging unit is in high-speed rotation. However, since the rotary element slides with the contact of the slip ring, problems arise in the slip ring such as abrasion and deterioration of the rotary element and the contact and a contact failure between the two due to their own vibration. Preferably, these problems should be solved from the standpoint of accurate, reliable signal transfer.
In order to solve such problems, Japanese Laid-open Patent Publication No. 2004-111696 for example discloses an optical slip ring which can perform signal transfer in a non-contact manner. Such a slip ring comprises optical transmitter systems and receiver systems on both a fixed member (equivalent to the base unit in the above example) and a rotary member (equivalent to the ranging unit in the above example) so that they face the rotary axis. Such a slip ring can transfer signals between the fixed member and the rotary member relatively rotated by receiving the optical signal from the transmitter system of the fixed member with the receiver system of the rotary member even with a change in a rotary position of the rotary member relative to the fixed member.
There is a surveying apparatus which includes a laser beam emitter in a ranging unit rotatably supported on a base unit to emit a laser beam in a direction orthogonal to the rotary axis. Such a surveying apparatus is configured to emit a laser beam to an object, receive a reflected light therefrom with a light receiver system, and measure an incidence angle of a light receiving position relative to a plane orthogonal to the rotary axis and a height from the emission position. In order to improve the measuring accuracy of the incidence angle and height, the surveying apparatus needs to reduce shifts of a laser beam from the rotary axis as much as possible. Because of this, in the surveying apparatus the ranging unit accommodates a mirror on the rotary axis and a laser light source is secured on a base unit to emit a laser light to the mirror along the rotary axis.
Such a surveying apparatus cannot adopt an optical slip ring for positioning optical receiver systems/transmitter systems on both of the fixed member (base unit) and rotary member (ranging unit) on the rotary axis since it includes the laser beam emitter in the space around the rotary axis of the base and the ranging unit.